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Displaying posts with tag: metadata locks (reset)

Exploring MySQL Metadata Lock Instrumentation in Closer Detail
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I recently wrote a post on tracking metadata locks (MDL) in MySQL 5.7, and I wanted to take a moment to expand on it by explaining a couple of the associated variables in more detail.

First off, once you have enabled the performance_schema *and* the metadata lock instrumentation, you can verify it with:

mysql> SELECT * FROM performance_schema.setup_instruments
    -> WHERE NAME = 'wait/lock/metadata/sql/mdl';
+----------------------------+---------+-------+
| NAME                       | ENABLED | TIMED |
+----------------------------+---------+-------+
| wait/lock/metadata/sql/mdl | YES     | YES   | …
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Mitigating the Effect of Metadata Lock (MDL) Contention
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If you see the “Waiting for table metadata lock” error, you may be wondering what is the best course of action to prevent it in the future. I have briefly discussed troubleshooting metadata locks before, however, that post more illustrated how easy it is to encounter the “Waiting for table metadata lock” error in both MyISAM and InnoDB. It provides simple examples for reproducing using both storage engines, so one could hopefully more easily identify where the locks are stemming from in their particular case.

Pin-pointing which transaction holds the locks is a different story. There are feature requests …

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